The present invention relates generally to interface devices between humans and computers, and more particularly to computer interface devices that provide force feedback to the user.
Interface devices are used extensively with computer systems in the implementation of computer-controlled games, simulations, and other applications very popular with the mass market of home consumers. In a typical implementation, a computer system displays a visual environment to a user on a display device. Users can interact with the displayed environment by inputting commands or data from the interface device. Popular interface devices include joysticks, xe2x80x9cjoypadxe2x80x9d button controllers, mice, trackballs, styluses, tablets, pressure spheres, foot or hand pedals, or the like, that are connected to the computer system controlling the displayed environment. The computer updates the environment in response to the user""s manipulation of a moved manipulandum such as a joystick handle or mouse, and provides visual feedback to the user using the display screen.
In some interface devices, haptic (e.g., tactile) feedback is also provided to the user, more generally known as xe2x80x9cforce feedback.xe2x80x9d These types of interface devices can provide physical sensations to the user manipulating the physical object of the interface device. Typically, motors or other actuators of the interface device are coupled to the manipulandum and are connected to the controlling computer system. The computer system receives sensor signals from the interface device and sends appropriate force feedback control signals to the actuators in conjunction with host events. The actuators then provide forces on the manipulandum. A local microprocessor can be used to off load some computational burden on the host. The computer system can thus convey physical sensations to the user in conjunction with other visual and auditory feedback as the user is contacting the manipulandum. Commercially available force feedback devices include the ForceFX joystick from CH Products, Inc. and Immersion Corporation, and the Sidewinder Force Feedback Pro from Microsoft Corporation.
One problem occurring in the commercially available force feedback devices is the free movement of the manipulandum, such as a joystick handle, when the device is not powered. For example, standard joysticks without force feedback capability typically include physical springs coupled between the joystick handle and the joystick base which provides a spring force on the handle and permanently functions to center the joystick handle in its degrees of freedom, causing the handle to be biased toward a straight and upright position and assisting in playing games. Force feedback joysticks, however, do not include such physical springs. This is because the forces provided by physical springs can interfere with the forces generated by the actuators of the force feedback device, which can greatly reduce the fidelity of generated forces. For example, if a vibration is to be output on the joystick, the force designer may not want a spring force from physical springs to be felt which would interfere with the vibration. However, a problem caused by the lack of physical springs in force feedback joysticks is that the joystick handles are not centered in an upright or other desired position. Although simulated spring forces can be output by the actuators to perform this centering function during normal joystick operation, it remains a problem when the joystick is not powered. For example, store owners or other vendors often display demonstration force feedback joysticks on shelves for users to test the way the handle grip feels. The demonstration joysticks are typically not powered, and since no physical springs are included, the joystick handles are tilted to one side, giving the undesired appearance of a faulty or broken joystick. In addition, spring forces on normal demonstration joystick models give the user an indication of how the joystick feels during normal operation when spring forces are present, which is not possible with unpowered force feedback joysticks. In other situations, the user may not be powering a force feedback joystick for some reason while playing a game, and the nornal centering spring forces would not be present on the handle, thus inhibiting game play.
A different problem occurs in force feedback peripherals having a force transmission mechanism such as a cable drive. In some cable drive systems, an actuator transmits forces to a manipulandum by rotating a cable attached to a capstan drum, where the drum is coupled to the manipulandum. The cable typically rides along the end of the drum as the drum is rotated by the actuator. However, if the capstan drum is rotated too far, the cable can move off the end or side of the drum, causing the transmission system to become inoperative. A different problem with the cable is keeping it correctly tensioned on the drum. When the cable has one or two ends that are rigidly attached to points on the drum, the assembly process for the system can become time consuming and expensive due to the requirements for tensioning the system. In addition, the cable typically requires re-tensioning as it becomes loose over time from use. Other problems occurring in commercially available force feedback devices include inaccuracies involved with sensing the position of the manipulandum and outputting forces on the manipulandum, such inaccuracies often contributed by plastic or other flexible components used in low-cost devices.
The present invention provides a force feedback interface device which includes several improvements to the force transmission system. One feature is the use of selectively engageable physical springs which center the force feedback manipulandum when the device is not outputting forces. Other features include a capstan drive mechanism including a cable tensioned by a spring at both ends of the cable, and a capstan drum including flanges for preventing the cable from moving off the side of the drum.
More particularly, a mechanism of the present invention for providing selective engagement of spring members to a user manipulatable object in a force feedback interface device includes a grounded member coupled to a grounded surface, a moveable member included in a force feedback mechanism and moveable in a degree of freedom to transmit forces to a user manipulatable object of the force feedback interface device, and a spring member that can be selectively coupled and selectively decoupled between the grounded member and the moveable member. The spring member preferably provides a spring force on the moveable member that biases the user manipulatable object to a desired position, such as the center of the degree of freedom. The force feedback interface device, including its mechanism, sensors, and actuators, can take a variety of forms.
In one embodiment, a catch mechanism is coupled to the spring member and includes first and second catch members. The first catch member may be selectively engaged and disengaged with the grounded second catch member, e.g. using a latch, and the first and second catch members are coupled to opposite ends of the spring member. The first catch member can include one or more receptacles for receiving pegs coupled to the moveable member. When the spring member is engaged to apply a spring bias to the manipulandum, the peg engages the receptacle as the moveable member is moved. When the spring member is disengaged so that no spring bias is applied to the manipulandum, the first catch member has been moved such that the peg does not engage the receptacle as the moveable member is moved. The first catch member is preferably moveable by a user of the interface device to selectively engage said spring members with the manipulandum, e.g. a portion of the first catch member can extend through an opening in a housing of the force feedback interface device for access by the user. Thus, the catch mechanism that provides the spring return on the manipulandum is also preferably the catch mechanism moved by the user, allowing fewer parts to be used.
A dynamic calibration procedure of the present invention for reducing inaccuracies when sensing the position of the user manipulandum is also preferably employed in a device using, for example, a transmission system such as described herein implemented with semi-flexible materials such as plastic. The dynamic calibration procedure normalizes the sensed position of the user manipulandum based on the range of manipulandum movement sensed up to the current point in time. To prevent detecting a xe2x80x9cfalsexe2x80x9d limit caused by an actuator. overstressing the transmission system, the calibration procedure preferably only reads new range limits when the actuator is not outputting a force in the direction of that limit.
A method of the present invention for selectively providing a spring force in a force feedback interface device using a physical spring includes providing a spring member between the user manipulandum and a linkage mechanism, selectively decoupling the spring member from the manipulandum when an actuator of said interface device is to output forces on the manipulandum, and selectively coupling the spring member to the manipulandum when the actuator is not to output forces on the manipulandum.
In a different aspect of the present invention, a force feedback interface device coupled to a host computer and providing forces to a user manipulating the interface device includes a user manipulandum for physical contact by a user, a sensor for detecting a position of the manipulandum, an actuator for applying a force to the manipulandum, and a linkage mechanism providing a degree of freedom and transmitting force from the actuator to the manipulandum. Furthermore, a capstan drive mechanism is coupled between actuator and linkage mechanism and includes a capstan pulley, a moveable capstan drum, and a cable coupling the pulley to the drum. In one aspect of the present invention, the capstan drum includes a curved end over which the cable is routed, the curved end including flanges arranged on sides of the curved end to substantially prevent the cable from slipping off the sides of the end. The curved end is preferably a sector, i.e., a portion of a circumference of a cylinder. In a different aspect of the present invention, the capstan drum includes a tensioning spring member coupled to one or both ends of the cable for tensioning the cable.
The improvements of the present invention provide a more versatile and durable force feedback interface device. The selective spring mechanism provides a mechanical spring bias on the user manipulandum in instances when forces are not output or power is not provided to the device, yet allows high-fidelity forces to be transmitted during normal operation by decoupling the spring bias. The capstan drive improvements allow for a more durable drive transmission that reduces problems that might occur with a cable drive, such as the cable becoming loose or the cable slipping from a capstan drum. The dynamic calibration procedure addresses inaccuracies of a described embodiment of the device. These improvements allow a low-cost force feedback device to be more reliable and versatile.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following specification of the invention and a study of the several figures of the drawings.